Process for the extraction of cadmium as sulphate



Patented 9 v UNITED srArss r cries;

P A T E JOHN BURNS READ AND MELVILLE F. COOLBAUGH, 0F DENVER, COLORADO.

PROCESS FOB, THE EXTRACTION 0F CADMIUM AS SUIEHA'IE.

Io Drawing. Application filed January To all whom it may concern:

Be it known that we, J onu Bonus Reno and F. GOOLBAUGE, citizens of the United States, residing at Denver in the county of Denver and State of dolorado, have invented certain new and useful Improvements in Processes for the Extraction of Cadmium as Sulphate, of which the folf. 1

lowing is a specification.

The object of this invention is to recover cadmium es sulphate from flue dust and other materials which contain arsenic as well as cadmium, and to free the cadmium from such arsenic and other impurities.

Heretofore two methods have been employed in general for treatment of fine dust to recover cadmium therefrom. The first of these consists in driving 03 as much of the arsenic as possible by a preliminary roast, and, then treating the mass with sulphuric acid followed by roasting at eternperature rangingbetween 300 C. and 700 C. to form cadmium and other sulphates and to decompose and drive off the excess sulphuric acid. The product isthen leached -with water to dissolve the cadmium sulphate which is Water soluble. But by this procedure a large proportion of the cadmium always remains in the residue united with the arsenic as cadmium arsenate If this residue be treated withsulphuric acid, much of the cadmium will be taken. into solution, but along with it there will also be obtained much of the arsenic in solution which must be separated by diiiicult methods before the cadmium can be obtained in mar ketable condition. The second of the two methods consists in dissolving the cadmium and arsenic as completely as possible with sulphuric acid, and then precipitating the arsenic by neutralizim he solution with an alkali in the presence or a ferric salt to obtain ferric arsenate. But the ferric arsenate .so precipitated is a bulky colloidal mass which is very difiicult to filter and Wash, and therefore retains large amounts of the endmium. This finely colloidal massis also more or less readily washed through the filter, thereby contaminating the filtrate containing the dissolved. cadmium sulphate. Thus, neither of these'* 1. thods has been satisfactory either as'to percentage of recovery or as to manipulation.

In one form of the present process, lIOIl pyrites is added to the flue dust or other cadmium and, arsenic bearing materials in 2, 192%. Serial Ho. 684.086.

quantity somewhat more than equivalent to the arsenic present, and the mixture is roasted at a temperature which may range between 450 C. and 700 C; to produce ferric oxide for the subsequent formation of ferric arsenate, and to drive off as much as iOSSlblG ofwthe arsenous oxide (A550 as sue and also in the form of arsenous sulphide (AS 8 This initial roast in its early stages is preferably made with only a ,j'small uantity of air, which condition is most e active for the elimination of arsenic; but is finished under highly oxidizing conditions with an excess of air to form ferric oxide. Sulphuric acid is then mixed with.

the roasted materials in uantity somewhat greater {than the chemical equivalent of the metal oxides present, and this mass is roasted at a temperature between 300 C. and 700 C. until the major portion or all ,of the excess sulphuric acid is decomposed and driven oh. This. treatment results in the formation of lead and cadmium sulphates, the latter being soluble, and causes the remaining arsenic to combine with the ferric iron (Fe O to form a ferric arsenate in the dry way which is quite granular in nature is insoluble in water and is filtered easily. From the insoluble, granular ferric arsenate thus formed, and any lead or other in soluble sulphates present, the soluble cadmium sulphate is readily leached with water, and a very high percentage recovery of the cadmium is obtained. Y 1

While the object of the initizil roast of the flue dust with the pyrites is for the purpose of eliminating arsenic and ultimately forming ferric oxide (Fc O there are also formed some cadmium and lead sulphates, and some cadmium and lead arsenatcs, along with some other sulphates and arsenates. These sulphates permit a corresponding decrease in the amount of sulphuric acid required in the next step for complete conversion of cadmium, lead and other metals to sulphates with the accompanying conversion of all the arsenic into ferric arsenate. When relatively large amounts of pyrites are used and most of the arsenic driven 01?, it is possible to form large quantities of cad mium sulphate which can be leached with water, thus eliminating; the treatment with sulphuric acid. In order to accomplish the I a praisin cadmium with? I can be treated on the top imposed hearth roaster which is sealed from pyrite, the ;,eharge earth of a super- I the lower hearths. Thetcmperatureon this flue dust will vary pyrite ,andthe' arsenic and tents-of the flue dust. Mixtures varying to treatthe flue dust ,in a prelimina hearth *should be from 450 o 7 0 -,degrees 'centigrade',. and (only a "small quantity of ail-admitted during the treatment. This will efiec't a very complete elimination of the arsenic which is taken off in an independent fiue.-- he dust then to the lower .hearths'"where more pyrite may he added,

where air is admitted, .where ferric. oxide is formed and where, for most eificient conversion ofthe-cadmium to sulphate, -the gases and mineral charge travel 111 the same direction, or concurrentlyand are subjected to a temperature that may range between'350 C. and 750 C. 'l'hBfiOPOI'tlOllgOf pyrite tweenwide limits, depending upon the sulphur, content ofthe from one part pyrite tofour parts of. dust to one and one-half arts pyrite toone part of dust have prov efliclent, combinations ior different materials used.

F or economic reasons, it ay be desirable before addition of'the 'i'ron pyrites or the of the arsenious oxide as possible, the tempurpose of eliminating at this point as much perature for this operation may range between 450" C. and 7 00 G. The pyrites may then be added and-the roast continued to" ield ferric oxide .asabove, this being folowed'by either a water leach or the sul- "phuric acid roast. Thus the roast of the dust before and after addition of the pyrites results in the, elimination of the great- .est amount of'a'rseniousoxide, which is 001-" a lected in the line and recovered.-

- Where ferric oxide mayheobtained economically'the process may he carried thereon without the use of. pyrites. "In this iii-- ;,driveofl arsenious oxi e, and then mixed stance the flue dust ma first be roasted to .with the ferric oxide and roasted. Or either B0 be; usedordinarily.

629,-512,fi1ed.Ap

and claimeda M has: ,ca

or both of theseroasts may be omitted. 1 The l ferric oxideand the flue dust are thenmixed with sulphuric acid and the 'r'oa'sthetween 300? (I. and 700 C. is carried ones with the other methods with the same results. It

will also be possible to use. ferric sul hate and vother iron compounds, which w1 1 be -mixed with the flue-dust and sulphuric acid and 'roast'ed to convert the cadmium and arsenic .to cadmium sulphate and ferric ar senate, as above.- ordinarily available and much chea er than the other iron compounds and there ore-will application, Serial No. 2, 1923,-we heave disclosed for the extraction 0 dmium as phatefromarsenic and. cadric arsenate from which the cadmium conroast However, iron pyrites are r f between 450 and 700 C. to .drive 0' -;miun 1 containing conipouands comprising roasting said compoun s with iron pyrites to form fernc oxide, mixing sulphurgih acid wlththe roasted materials and ro'asti the -mixture to drive or the excess sulp uric acid and form cadmium sulphate and a farcadmium sulphate maybe readily leached.

We claim- 1.'The process for the recovery of cadm um as sulphate from arsenicand cad-, mlum-bearlng materials which includes .roastingthe materials with iron-containing sulphate-forming material to produce cadmium sulphate.

' 2. The process for the recovery ofcadmium as sulphate from arsenic and cadmium-bearing materials which includes add- .ing iron sulphur containing material to said arsenicand cadmiumrbearing materials roasting the same to drive 01f arsenic an convert the cadmium to sulphate. 3.' The process for the recovery of cadmium as sulphate from arsenicand cad mium-bearing materials which includes adding iron sulphur containing material to said arsenicand cadmium-bearing materials roastin the same to drive ofi arsenic and afterwards roasting the resultant products to convert the cadmium to sulphate.

4. The process for the recovery of cadmium as sulphate from arsenicand cadmium-bearing materials which includes adding iron sulphur containing material to said rial and efi'ecting thereby the conversion of cadmium-to cadmium sulphate. 6. The process for the recovery of cadmium as sulphate from arsenicand cadmium-hearing materials com rising roastingrthe materials with a re atively small amount of air to drive off arsenic, and then continuin the roast of the. cadmium-bearing materials mixed with iron sulphur con-' taming material and a greater amount of air'and effecting thereby the conversion ofcadmium to; cadmium sulphate I 7.'The process for the recovery of cad mium as sulphate from arsenic-- and cadmium bearing materials; com rising roast ing the -material vwith a re atively small amount of air and at a temperature ran 'ng arsenic and. 'reroasting the cadmium-bearing materials mixed wit}; iron sulphur containmg materlal and wlth a greater amount oi an' and effec'sm thereby the converslon of cacimium to ca mium sulphate.

8. The process for the recovery of did- 7 mium as sulphate from arsenic and cadranging between 450 C. to 700 0. thereby 1 driving ofi' arsenic and afterwards wasting the mixture and thereby converting the cadznium to cadmium sulphate. t In te'stimony whereof, we aifix'our signaures.

JOHN BURNS READ. MELVILLE F. OOOLBAUGH. 

